This invention relates to a printer for use in information processing and electric communication and a method of developing a latent image printed on the printer.
For use in a personal terminal device or in a monitor, a page or a line printer is preferably capable of printing a clear print at a high speed and quietly. The printer should furthermore be small-sized, simple in structure, and suitable for production on a large scale.
An impact printer is operable to print out an image on a usual paper and is adapted to general purposes. The impact printer is, however, noisy and operable to print unclear and at a low speed. As a consequence, either an ink-jet printer or a thermographic printer is used in many cases.
For a higher clarity and a higher speed, electrophotographic printers are in practical use. In such an electrophotographic printer, use is made of an electrostatic latent image or an image of residual polarization in a ferroelectric layer.
Among the printers described in the foregoing, the thermographic printer and the ink-jet printer are suitable for use as a built-in printer of a personal computer. That is, either of the thermographic and the ink-jet printers is simple in structure and compact and is, above all, of a small height.
use of the residual polarization in a ferroelectric layer is disclosed in, for example, Japanese Patent Prepublications (A) Nos. 269,155 of 1987, 269,156 of 1987, and 18,369 of 1988. In each of these prior patent applications, the ferroelectric layer is formed either on a drum or a movable plate. Polarization in the ferroelectric layer is inverted either electrically or both thermally and electrically into a latent image of residual polarization. For supply of an electrostatic toner to the latent image, a developing device comprises a specific brush.
Use of the residual polarization is revealed also in Japanese patent Prepublication (A) No. 220,177 of 1988. In this printer, the ferroelectric layer is formed on an electroconductive substrate. Polarization in this ferroelectric layer is electrically inverted. It is possible to get a plurality of prints from a single latent image.
At any rate, use of such residual polarization in a ferroelectric layer or film is excellent. This is because, the latent image is developed with use of neither a high voltage generator nor a large-capacity memory for processing the image.
Conventional printers of this residual polarization type are, however, defective in several points. In the manner described above, the residual polarization is controlled either electrically or thermally. It is therefore necessary to put either an electrode or a head for electric or thermal processing in a position where the residual polarization is inverted. Alternatively, the ferroelectric layer must be put near to the electrode or the head. For high-speed printing, such movement must be rapid and precise. In addition, the printer becomes bulky and difficult to implement as the height is reduced.
Furthermore, the residual polarization has been inverted by application of an electric field to the ferroelectric layer. For this purpose, the ferroelectric layer must be either brought into contact with an electrode or subjected to electric discharge in, for example, gas. Use of the thermal processing must similarly be carried out. This results in a wear-out or a damage of the ferroelectric layer and eventually in a short serviceable life of the printer.